U.S. patent application number 11/544040 was filed with the patent office on 2007-02-08 for chemical treatment of biological samples for nucleic acid extraction and kits therefor.
This patent application is currently assigned to Becton, Dickinson and Company. Invention is credited to Matthew P. Collis, Thomas L. Fort, Jianrong Lou.
Application Number | 20070031880 11/544040 |
Document ID | / |
Family ID | 32823787 |
Filed Date | 2007-02-08 |
United States Patent
Application |
20070031880 |
Kind Code |
A1 |
Lou; Jianrong ; et
al. |
February 8, 2007 |
Chemical treatment of biological samples for nucleic acid
extraction and kits therefor
Abstract
A composition and method for the purification of nucleic acid
are disclosed. The composition includes at least one alkaline agent
and at least one detergent. The composition preferably also
includes a suspension of paramagnetic particles and an acidic
solution. The method involves the use of the composition with
paramagnetic particles to extract nucleic acid from a biological
sample.
Inventors: |
Lou; Jianrong; (Mount Airy,
MD) ; Collis; Matthew P.; (Seven Valleys, PA)
; Fort; Thomas L.; (Finksburg, MD) |
Correspondence
Address: |
DAVID W HIGHET VP AND CHIEF IP COUNSEL;BECTON DICKINSON AND COMPANY
1 BECTON DRIVE
MC110
FRANKLIN LAKES
NJ
07417-1880
US
|
Assignee: |
Becton, Dickinson and
Company
|
Family ID: |
32823787 |
Appl. No.: |
11/544040 |
Filed: |
October 6, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10359180 |
Feb 6, 2003 |
|
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11544040 |
Oct 6, 2006 |
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Current U.S.
Class: |
435/6.14 ;
536/25.4 |
Current CPC
Class: |
C07H 21/04 20130101;
C12N 15/1013 20130101 |
Class at
Publication: |
435/006 ;
536/025.4 |
International
Class: |
C12Q 1/68 20060101
C12Q001/68; C07H 21/04 20070101 C07H021/04 |
Claims
1. A method for purifying nucleic acid from a biological sample,
comprising: (a) treating said biological sample with at least one
alkaline agent and at least one detergent; (b) providing a
suspension of at least one paramagnetic particle; (c) providing an
acidic solution; and (d) combining said suspension and said acidic
solution with said treated biological sample such that at least one
nucleic acid molecule in said biological sample is reversibly bound
to said at least one paramagnetic particle.
2. The method of claim 1, wherein said at least one paramagnetic
particle comprises iron.
3. The method of claim 1, wherein said at least one paramagnetic
particle is selected from the group consisting of an iron oxide,
iron sulfide and iron chloride.
4. The method of claim 3, wherein the iron oxide is selected from
the group consisting of ferric hydroxide and ferrosoferric
oxide.
5. The method of claim 1 further comprising: (e) eluting said at
least one nucleic acid molecule from said at least one paramagnetic
particle.
6. The method of claim 5, wherein said eluting comprises contacting
said reversibly bound nucleic acid with a reagent selected from the
group consisting of Tris, Bicine, CAPS, HEPES, water, potassium
phosphate, Tricine, and assay buffers.
7. The method of claim 5 further comprising: (f) detecting said at
least one nucleic acid molecule.
8. The method of claim 5 further comprising: (f) amplifying said at
least one nucleic acid molecule after eluting.
9. The method of claim 1, wherein the alkaline agent is selected
from the group consisting of KOH, NaOH, NH.sub.4OH and
Ca(OH).sub.2.
10. The method of claim 1, wherein the detergent is selected from
the group consisting of anionic, nonionic and zwitterionic
detergents.
11. The method of claim 10, wherein the anionic detergent is
selected from the group consisting of sodium dodecyl sulfate and
lithium dodecyl sulfate.
12. The method of claim 10, wherein the nonionic detergent is
selected from the group consisting of polyethylene glycol sorbitan
monolaurate, polyethylene glycol sorbitan monooleate, NP-40,
polyethylene glycol tert-octylphenyl ether and cetyl trimethyl
ammonium bromide.
13. The method of claim 10, wherein the zwitterionic detergent is
selected from the group consisting of
3[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate and
zwitterionic surfactants.
14. The method of claim 1, wherein said alkaline agent and said
detergent are added to bring said biological sample to a pH of
about 7 to about 12.
15. The method of claim 1, further comprising extracting said
nucleic acid with an acid selected from the group consisting of
phosphoric acid, nitric acid, hydrochloric acid, sulfuric acid,
acetic acid and citric acid.
16. The method of claim 1, wherein potassium phosphate is
employed.
17. The method of claim 1, wherein said nucleic acid is selected
from the group consisting of DNA and RNA.
18. The method of claim 1, wherein said biological sample is
selected from the group consisting of whole blood, plasma, serum,
urine, semen, feces, finger nails, skin, sputum, nasopharangeal
aspirates, and swabs, including endocervical, vaginal, occular,
throat and buccal swabs, hair, cerebrospinal fluid, tissue, cell
culture and cell suspension.
19. A composition for purifying nucleic acid from a biological
sample, the composition comprising at least one alkaline agent; at
least one detergent; and at least one paramagnetic particle;
wherein the at least one alkaline agent and the at least one
detergent are present in concentrations that can denature proteins
and lyse infectious agents.
20. The composition of claim 19, wherein the composition comprises
a suspension of the at least one paramagnetic particle.
21. The composition of claim 20, further comprising an acidic
solution.
22. The composition of claim 19, wherein said alkaline agent and
said detergent are in a liquid solution.
23. The composition of claim 19, wherein said alkaline agent and
said detergent are in dry form.
24. The composition of 19, wherein the alkaline agent is KOH and
the detergent is polyethylene glycol tert-octylphenyl ether.
25. A kit for purifying nucleic acid from a biological sample, the
kit comprising: at least one alkaline agent; at least one
detergent; and at least one paramagnetic particle; wherein the at
least one alkaline agent and the at least one detergent are present
in concentrations that can denature proteins and lyse infectious
agents.
26. The kit of claim 25, wherein the kit comprises a suspension of
at least one paramagnetic particle.
27. The kit of claim 26, further comprising an acidic solution.
28. The kit of claim 24, wherein the alkaline agent is KOH and the
detergent is polyethylene glycol tert-octylphenyl ether.
29. The method of claim 5, wherein said eluting is conducted at a
pH of about 7 to about 12.
30. The method of claim 1, wherein said alkaline agent and said
detergent bring said biological sample to a pH of about 7 to about
12 in step (a).
31. The method of claim 1, wherein said acidic solution brings said
biological sample/alkaline agent/detergent to a pH of about 1 to
about 7 in step (c).
32. The composition of claim 19, wherein said alkaline agent is
present in an amount from about 10 mM to about 400 mM.
33. The composition of claim 32, wherein said detergent is present
in an amount from about 0.05% to about 10.0% by volume.
34. The method of claim 8, wherein said method is performed in a
single vessel.
35. The method of claim 34, wherein said providing a suspension of
at least one paramagnetic particle comprises adding said biological
sample to said single vessel.
36. A composition for purifying nucleic acid from a biological
sample, the composition comprising: at least one alkaline agent; at
least one detergent; and at least one paramagnetic particle;
wherein the at least one alkaline agent is present in the
composition in an amount from about 10 mM to about 400 mM, and the
at least one detergent is present in an amount from about 0.05% to
about 10.0% by volume.
37. A kit comprising the composition of claim 36.
38. The composition of claim 36, wherein the alkaline agent is KOH
and the detergent is polyethylene glycol tert-octylphenyl
ether.
39. The composition of claim 36, wherein the alkaline agent is KOH
and the detergent is polyethylene glycol tert-octylphenyl ether.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to extraction, isolation or
purification of nucleic acids (i.e., DNA or RNA) from plasma, whole
blood and other biological samples by paramagnetic surface binding
or other nucleic acid extraction methods. Extracted nucleic acid
can be used for various DNA/RNA applications such as nucleic acid
amplification and/or detection for the diagnosis of disease.
BACKGROUND OF THE INVENTION
[0002] Access to cellular components such as nucleic acids is
imperative to a variety of molecular biology methodologies
including nucleic acid sequencing, direct detection of particular
nucleic acid sequences by nucleic acid hybridization and nucleic
acid sequence amplification techniques. The extraction, isolation
or purification of DNA or RNA is an important step in many
biochemical and diagnostic procedures. For example, the extraction
and separation of nucleic acids from the complex mixtures in which
they are often found is frequently necessary before other studies
and procedures, e.g., cloning, sequencing, amplification,
hybridization, cDNA synthesis, detection, etc., can be undertaken.
The presence of large amounts of cellular or other contaminating
material, e.g., proteins or carbohydrates, in such complex mixtures
often impedes many of the reactions and techniques used in
molecular biology. For example, plasma and whole blood are clinical
samples commonly used for nucleic acid-based diagnostics. High
protein levels and the high RNase/DNase levels are major obstacles
for processing such samples, as well as other samples having high
amounts of protein and/or RNase or DNase.
[0003] In addition, DNA may contaminate RNA preparations and vice
versa. Thus, methods for the extraction, isolation or purification
of nucleic acid from complex mixtures such as cells, tissues, etc.
is desirable, not only from the preparative point of view, but also
as part of the many methods in use today which rely on the
identification of DNA or RNA, e.g., clinical diagnosis, forensic
science, tissue and blood typing, detection of genetic variations,
etc.
[0004] A number of methods are known for the extraction, isolation
or purification of nucleic acids. Generally, such methods rely on a
complex series of extraction, isolation or purification steps,
which are time consuming and laborious to perform. Moreover, such
methods involve the use of materials such as alcohols and other
organic solvents, chaotropes and proteinases, which is
disadvantageous because such materials tend to interfere with many
enzymatic reactions and other downstream processing
applications.
[0005] Classical methods for the extraction, isolation or
purification of nucleic acid from complex starting materials such
as blood, blood products, tissues or other biological samples
involve lysis of the biological material by a detergent or
chaotrope, possibly in the presence of protein degrading enzymes,
followed by several extractions with organic solvents, e.g., phenol
and/or chloroform, ethanol precipitation, centrifugation and
dialysis of the nucleic acids. The purification of RNA from DNA may
involve additional steps, for example, selective precipitation with
LiCl or selective isolation with acidic guanidinium thiocyanate
combined with phenol extraction and ethanol precipitation. Not only
are such methods cumbersome and time consuming to perform, but also
the relatively large number of steps required increases the risk of
degradation, sample loss or cross-contamination of samples where
several samples are simultaneously processed. In the case of RNA
isolation, the risk of DNA contamination is relatively high. The
purification of double-stranded plasmid DNA, single-stranded phage
DNA, chromosomal DNA, agarose gel DNA fragments and RNA is of
critical importance in molecular biology. Ideally, a method for
purifying nucleic acids should be simple, rapid and require little,
if any, additional sample manipulation. Nucleic acids obtained by
such a method should be immediately amenable to transformation,
restriction analysis, ligation or sequencing. A method capable of
providing DNA or RNA of high purity is, therefore, highly
desirable.
[0006] Another purification method for preparation of plasmid DNA
from crude alcohol precipitates is laborious, most often utilizing
CsCl gradients, gel filtration, ion exchange chromatography, and
repeated alcohol precipitation steps. These methods also require
considerable downstream sample preparation to remove CsCl and other
salts, ethidium bromide and alcohol. A further problem with these
methods is that small, negatively charged cellular components can
co-purify with the DNA. Thus, the DNA can have an undesirable level
of contamination.
[0007] Nucleic acids can also be purified using solid phases.
Conventional solid phase extraction techniques have utilized
silica-type surfaces that either (1) fail to attract and hold
sufficient quantities of nucleic acid molecules to permit easy
recovery, or (2) excessively adhere to the nucleic acid molecules,
thereby hindering their recovery. Conventional surfaces that cause
these problems include surfaces such as glass and Celite. Adequate
binding of nucleic acids to these types of surfaces can be achieved
only by utilizing high concentrations of chaotropes or alcohols,
which are generally toxic, caustic, and/or expensive. For example,
it is known that DNA will bind to crushed glass powders and to
glass fiber filters in the presence of chaotropes. The chaotropic
ions typically are washed away with alcohol, and the DNA is eluted
with low-salt solutions or water. A serious drawback in the use of
crushed glass powder is that its binding capacity is low. In
addition, glass powder often suffers from inconsistent recovery,
incompatibility with borate buffers and a tendency to nick large
DNAs. Similarly, glass fiber filters provide a nonporous surface
with low DNA binding capacity. Other silica-type surfaces, such as
silica gel, hydrated and hydroxylated silica surfaces as disclosed
in EP 0512767 and U.S. Pat. Nos. 5,674,997, 5,693,785 and
6,355,792, do not require chaotropic agents for surface
binding.
[0008] There are numerous protocols for purifying DNA. For example,
U.S. Pat. No. 4,923,978 discloses a process for purifying DNA in
which a solution of protein and DNA is passed over a hydroxylated
support, the protein is bound and the DNA is eluted. U.S. Pat. No.
4,935,342 discloses purification of DNA by selective binding of DNA
to anion exchangers and subsequent elution. U.S. Pat. No. 4,946,952
discloses DNA isolation by precipitation with water-soluble
ketones. A DNA purification procedure using chaotropes and dialyzed
DNA is disclosed in U.S. Pat. No. 4,900,677.
[0009] Diatoms have also been utilized for purification of nucleic
acids as evidenced by U.S. Pat. No. 5,234,809 and U.S. Pat. No.
5,075,430. U.S. Pat. No. 5,234,809 discloses a method where nucleic
acids are bound to a solid phase in the form of silica particles in
the presence of a chaotropic agent such as guanidinium salt and
thereby separated from the remainder of the sample.
[0010] Although such methods speed up the nucleic acid separation
process, there are disadvantages associated with the use of
alcohols, chaotropes and other similar agents. Chaotropes are
generally used at a high molarity, resulting in viscous solutions
that may be difficult to work with, especially when working with
RNA. Amplification procedures such as the polymerase chain reaction
("PCR") and other enzyme based reactions are very sensitive to the
inhibitory or otherwise interfering effects of alcohols and other
agents. Moreover, the drying of the nucleic acid pellet, which is
necessary following alcohol precipitation, and the problems
associated with dissolving nucleic acids are also known to lead to
artifacts in enzyme-based procedures, such as PCR. Yet a further
technique utilized for purification of nucleic acids is binding to
specifically adapted paramagnetic particles. Examples of such
techniques may be found in references such as EP 0 446 260 B1 and
U.S. Pat. No. 5,512,439, which describe monodisperse,
superparamagnetic particles having a particle diameter standard
deviation of less than 5%. Each particle carries a plurality of
molecules of an oligonucleotide, with each oligonucleotide having a
section serving as a probe for a target nucleic acid molecule of
interest.
[0011] U.S. Pat. No. 4,672,040 and U.S. Pat. No. 4,695,393 describe
magnetically responsive particles for use in systems to separate
certain molecules. The particles have a metal oxide core surrounded
by a stable silicone coating to which organic and/or biological
molecules may be coupled.
[0012] U.S. Pat. No. 3,970,518 describes a method of sorting and
separating a select cell population from a mixed cell population.
The method utilizes small magnetic particles coated with an
antibody to select cell populations.
[0013] U.S. Pat. No. 4,141,687 describes an automatic apparatus and
method to assay fluid samples. The apparatus utilizes a particulate
material with a reagent bound thereto. The particulate material is
magnetic, and the reagent is a substance that takes part in a
reaction in the reaction mixture.
[0014] U.S. Pat. No. 4,230,685 describes a method for magnetic
separation of cells. The method utilizes magnetically responsive
microspheres coated with staphylococcal Protein A to which antibody
is bound.
[0015] U.S. Pat. No. 4,774,265 describes a process for preparing
magnetic polymer particles. The particles are compact or porous
polymer particles treated with a solution of iron salts.
[0016] U.S. Pat. No. 5,232,782 describes magnetizable "core-shell"
microspheres having a core of a magnetizable filler and a shell of
crosslinked organopolysiloxane.
[0017] U.S. Pat. No. 5,395,688 describes magnetically responsive
fluorescent polymer particles having a polymeric core coated evenly
with a layer of polymer containing magnetically responsive metal
oxide.
[0018] International Publication No. WO 96/18731 describes a method
for isolating nucleic acid from a sample using a particulate solid
support and an anionic detergent.
[0019] U.S. Pat. No. 5,705,628 describes a method for DNA
purification and isolation using magnetic particles with functional
group-coated surfaces.
[0020] International Publication No. WO 01/46404 discloses a method
for separating nucleic acid from a test sample that includes
contacting the sample with a metal oxide support material and a
binding buffer to form a nucleic acid/metal oxide support material
complex, separating the complex from the test sample, and eluting
the nucleic acid from the metal oxide support material. WO 01/46404
discloses that the buffer generally comprises a chaotropic agent
and a detergent.
[0021] U.S. Pat. No. 5,973,138, the entire contents of which are
incorporated herein by reference, discloses a composition that
reversibly binds a nucleic acid molecule. The composition includes
a paramagnetic particle in an acidic environment.
[0022] Iron oxide extraction of nucleic acid is non-specific, i.e.,
iron oxide binds nucleic acid irrespective of its form (RNA or DNA)
or sequence. Extraction of nucleic acid with iron oxide is less
efficient in highly proteinaceous mileus such as plasma. This may
be attributable to
[0023] competition between nucleic acid and protein for iron oxide
binding sites, (2) reduced kinetics due to higher viscosity of high
protein solutions, (3) the effect of endogenous sample nucleases on
nucleic acids, or (4) any combination of (1)-(3).
[0024] There is a need for improved methods of nucleic acid
extraction, isolation or purification and particularly for methods
that are quick and simple to perform and which avoid the use of
chaotropic agents or alcohol precipitation. There is also a need
for a method that permits isolation of both types of nucleic acid
from the same sample.
SUMMARY OF THE INVENTION
[0025] In order to provide a more effective and efficient technique
for the extraction, isolation or purification of nucleic acids, the
present invention provides a composition useful for extraction and
reversible binding of a nucleic acid molecule. The composition
comprises, in combination, at least one alkaline agent and at least
one detergent. In a preferred embodiment, the composition also
comprises a suspension of paramagnetic particles. In a more
preferred embodiment, the composition further comprises an acidic
solution.
[0026] The present invention also includes the composition packaged
as a kit, as well as methods utilizing the composition to
reversibly bind a nucleic acid molecule. The kit comprises a
package unit having one or more containers of the subject
composition. In some embodiments, the kit includes containers of
various reagents used with the subject composition to purify and
detect nucleic acid. The kit may also contain one or more of the
following items: collection devices such as swabs, pH indicators
and controls for processing and assaying the biological sample.
Kits may include containers of reagents mixed together in suitable
proportions for performing the methods in accordance with the
invention. Reagent containers preferably contain reagents in unit
quantities that obviate measuring steps when performing the subject
methods.
[0027] The method of the present invention involves extracting and
purifying nucleic acid from a biological sample comprising
contacting the sample with at least one alkaline agent and at least
one detergent; providing a suspension of at least one paramagnetic
particle; providing an acidic solution; and combining the
suspension and the acidic solution with the treated biological
sample such that at least one nucleic acid molecule in the
biological sample is reversibly bound to the at least one
paramagnetic particle. The desired DNA or RNA may then be eluted
from the at least one paramagnetic particle using the appropriate
buffer, e.g., Tris, Bicine, CAPS, HEPES, water, potassium
phosphate, Tricine, and assay buffers which may or may not contain
DMSO and/or glycerol. The method of the present invention has the
advantage over previous methods of processing of not requiring the
use of caustic agents such as chaotropes and alcohols.
[0028] Other features and advantages of the present invention will
be apparent from the following detailed description and also from
the appended claims.
DETAILED DESCRIPTION OF THE INVENTION
[0029] As used herein, the term "paramagnetic particles" means
particles capable of having a magnetic moment imparted to them when
placed in a magnetic field. Paramagnetic particles, when in such a
magnetic field, are movable under the action of such a field. Such
movement is useful for moving bound nucleic acid molecules for
different aspects of sample processing. Thus, nucleic acid
molecules bound to the paramagnetic particles can be processed as
desired with different reagents and/or conditions with minimal
direct contact due to the application of magnetic force.
[0030] As used herein, the terms "purifying" and "purification"
include extracting/extraction and isolating/isolation.
[0031] The present inventors have discovered that treating
biological samples with a combination of at least one alkaline
agent and at least one detergent prior to combination with the
paramagnetic particles allows protein denaturation to occur before
the sample makes contact with the paramagnetic particles.
[0032] The biological sample useful in the present invention may be
any material containing nucleic acid including, for example,
clinical, forensic and environmental samples. The sample will
generally be a biological sample that may contain any viral or
cellular material, including prokaryotic and eukaryotic cells,
viruses, bacteriophages, mycoplasms, protoplasts and organelles.
Such biological materials may thus comprise all types of mammalian
and non-mammalian animal cells, plant cells, algae including
blue-green algae, fungi, bacteria and protozoa. Representative
examples include whole blood and blood-derived products such as
plasma and serum, urine, semen, feces, finger nails, skin, sputum,
nasopharangeal aspirates, and swabs, including endocervical,
vaginal, occular, throat and buccal swabs, hair, cerebrospinal
fluid or other body fluids, including tissues, cell cultures and
cell suspensions.
[0033] The composition and method of the invention provide
advantages over prior known compositions and methods including more
rapid and more economical processing and the use of chemical rather
than enzymatic treatment. The composition and method of the
invention also permit the use of a higher sample volume. Prior
methods required dilution of a sample such as plasma by as much as
50% before enzyme digestion. In contrast, the present invention
permits extraction of nucleic acid from 100% plasma using
paramagnetic particles. The present invention also permits the
drying down of reagents, which can then be easily stored in tubes
and remain stable for long periods of time.
[0034] The composition of present invention denatures proteins and
lyses infectious agents such as viruses and bacteria during nucleic
acid extraction. It is believed that the combination of alkaline
agent and detergent inactivates RNases/DNases, which would
otherwise hinder the extraction of nucleic acid. The present
invention is thus directed to a composition that comprises at least
one alkaline agent and at least one detergent. The detergents that
are useful for the present invention include anionic, nonionic and
zwitterionic detergents. Suitable anionic detergents include, but
are not limited to, sodium dodecyl sulfate and lithium dodecyl
sulfate. Suitable nonionic detergents include, but are not limited
to, polyethylene glycol sorbitan monolaurate (i.e., Tween.RTM. 20),
polyethylene glycol sorbitan monooleate (i.e., Tween.RTM. 80),
NP-40, polyethylene glycol tert-octylphenyl ether (i.e., Triton X
detergents such as Triton X-20 and Triton X-100) and cetyl
trimethyl ammonium bromide (CTAB). Suitable zwitterionic detergents
include, but are not limited to,
3[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS)
and other zwitterionic surfactants. The alkaline agents useful in
the present invention include, but are not limited to, bases and
alkaline buffers such as KOH, NaOH, NH.sub.4OH and Ca(OH).sub.2,
phosphate buffers, saline buffers, borate buffers, Tris buffer and
the like.
[0035] The composition according to the present invention comprises
an alkaline agent in an amount of about 10 mM to about 400 mM and a
detergent in an amount of about 0.05% to about 10% by volume.
Preferably, the composition contains about 100 mM to about 200 mM
of an alkaline agent and about 0.1% to about 3.0% by volume of a
detergent.
[0036] According to one embodiment, the composition is in a liquid
solution and is placed in a container. According to another
embodiment, one or more of the components of the composition, alone
or in combination, may be dried by methods, such as vacuum drying
or freeze drying, that are known in the art. For example, by
freezing the solution and then slowly warming after freezing, while
simultaneously applying a vacuum, a freeze-dried powder remains in
the container, e.g., an extraction tube or a blood collection tube.
An additive such as an excipient, for example,
polyvinyl-pyrrolidone ("PVP") or trehalose, may also be added as a
stabilizing agent to the solution prior to drying so that the
resulting stabilizing agent is dried in the container. In another
aspect, the composition, or a subset of the composition, is formed
into a liquid or suspension and is dispersed or sprayed onto one or
more surfaces of the interior of the container.
[0037] The composition preferably includes a suspension of
paramagnetic particles. Iron particles are useful as the
paramagnetic particles in the present invention, and the iron may
be an iron oxide of forms such as ferric hydroxide or ferrosoferric
oxide. Other iron particles such as iron sulfide and iron chloride
may also be suitable for binding and extracting nucleic acids using
the conditions described herein.
[0038] The shape of the paramagnetic particles is not critical to
the present invention. The paramagnetic particles may be of various
shapes including, for example, spheres, cubes, ovals,
capsule-shaped, tablet-shaped, nondescript random shapes, etc., and
may be of uniform shape or non-uniform shape. Whatever the shape of
a paramagnetic particle, its diameter at its widest point is
generally in the range of from about 0.05 to about 20.0
microns.
[0039] The concentration of the particles may vary depending on the
biological sample. For most biological samples, the concentration
of the paramagnetic particles is about 1 mg/mL to about 500 mg/mL.
However, diluted sample or concentrated samples may need less or
more paramagnetic particles.
[0040] The composition of the present invention may further
comprise an acidic solution such as acids and acidic buffer
solutions. The acidic solution in combination with the paramagnetic
particles may then be used to extract the nucleic acid from
proteinaceous samples without clotting the sample. Any acid may be
used. Exemplary acids include, but are not limited to, phosphoric
acid, nitric acid, sulfuric acid, acetic acid and citric acid.
[0041] The acidic environment in which the paramagnetic particles
effectively and reversibly bind nucleic acid molecules can be
provided through a variety of means. For example, the paramagnetic
particles can be added to an acidic solution or an acidic solution
may be added to the particles. Alternatively, a solution or
environment in which the paramagnetic particles are located can be
acidified by addition of an acidifying agent. The acid is
sufficient to bring the pH of the alkaline agent/detergent
composition to an acidic pH, i.e., between about 1 to about 7.
[0042] As stated above, in an acidic environment, electropositive
paramagnetic particles will bind electronegative nucleic acid
molecules. Other materials in the environment, such as inhibitors
of nucleic acid hybridization and amplification can, therefore, be
separated from the bound nucleic acid molecules. Such separation
can be accomplished by means known to those skilled in the art,
such as centrifugation, filtering or application of magnetic
force.
[0043] The bound nucleic acid molecules can then be eluted into an
appropriate buffer for further manipulation, such as hybridization
or amplification reactions. Such elution can be accomplished by
heating the environment containing the particles with bound nucleic
acids and/or raising the pH of such environment. Agents which can
be used to aid the elution of nucleic acid from the paramagnetic
particles include water, buffers, alkaline agents such as KOH,
NaOH, NH.sub.4OH and Ca(OH).sub.2, phosphate buffers, saline
buffers, borate buffers, Tris buffer or any compound that increases
the pH of the environment to an extent sufficient that
electronegative nucleic acid is displaced from the particles.
[0044] The reversible binding and elution of nucleic acids on
paramagnetic particles is primarily achieved by altering the pH of
the media, in which the binding and elution procedures take place
following the alkaline agent/detergent pre-treatment. Nucleic acids
bind onto the surface of these particles in acidic pH and elute at
neutral or alkaline pH. However, there are other factors that also
affect the binding and elution. For example, reduced temperature
may increase binding of nucleic acids on the solid surface and
increased temperature may enhance the elution process. The
concentration of detergent used for the pre-treatment may also play
a role in nucleic acid binding. The combination of detergent and
alkaline agent treatment presumably (1) denatures proteins such as
DNases and RNases and (2) lyses cells and/or microorganisms such as
virions and/or bacterial cells. The concentrations of detergent and
alkaline agent should be high enough to disrupt the walls or
membranes of cells and virions, denature proteinaceous material and
solubilize the targeted nucleic acids.
[0045] The following example illustrates specific embodiments of
the invention. As would be apparent to skilled artisans, various
changes and modifications are possible and are contemplated within
the scope of the invention described.
EXAMPLE
[0046] The following example demonstrates the use of chemical
treatment and compares such treatment to enzymatic digestion during
extraction of HIV RNA from plasma. The efficiency of RNA extraction
was evaluated using an HIV SDA assay.
Treatment
[0047] 1. Dispense 22 mL of human plasma and 13.2 mL of 30 mM
KPO.sub.4 (pH 7.6) into a 50-mL tube.
[0048] 2. Add 80 .mu.g/mL of yeast carrier RNA into the tube.
[0049] 3. Spike the human plasma with HIV particles at the level of
1000 particles/mL.
[0050] 4. Mix well and dispense 16 mL of plasma mixture into two
tubes (tubes A and B).
[0051] 5a. In tube A, add 1.1 mL of Proteinase K (600 units/mL),
mixing well by inverting tube 6 times.
[0052] 5b. Incubate tube A in 70.degree. C. waterbath for 30
minutes.
[0053] 5c. Transfer 850 .mu.L of plasma mixture into 2-mL
extraction tubes containing 40 mg of iron oxide.
[0054] 5d. Mix by inverting tubes in 5-minute interval.
[0055] 6a. Dispense 800 .mu.L of plasma mixture from tube B into 16
extraction tubes containing 40 mg of iron oxide, 100 .mu.moles KOH,
and 10 .mu.L of Triton (these chemicals were dried down in
tubes).
[0056] 6b. Mix well by inverting tubes 6 times.
[0057] 6c. Incubate 8 tubes in a 70.degree. C. waterbath for 30
minutes.
[0058] 6d. Incubate another 8-tube set at room temperature for 30
minutes.
[0059] 6e. Mix by inverting tubes in 5-minute interval.
[0060] 7. Allow all tubes to cool down at room temperature for
another 30 minutes before extraction.
Binding and Elution
[0061] 1. Dispense 270 .mu.L of Binding acid (either 6 M
glycine.HCl or 6 M H.sub.3PO.sub.4) into tubes and mix 25
times.
[0062] 2. Magnetically lock iron oxide particles to the sides of
tubes.
[0063] 3. Aspirate the unbound sample.
[0064] 4. Wash the iron oxide particles with 1020 .mu.L of 1 mM of
glycine.HCl or 1 mM H.sub.3PO.sub.4.
[0065] 5. Magnetically lock the iron oxide particles and aspirate
the unbound solution.
[0066] 6. Wash iron oxide particles with 1020 .mu.L of 1 mM of
glycine.HCl or 1 mM H.sub.3PO.sub.4.
[0067] 7. Magnetically lock the iron oxide particles and aspirate
the unbound solution.
[0068] 8. Dispense 120 .mu.L elution buffer (85 mM KOH/75 mM
Bicine) into the tube and mix 15 times.
[0069] 9. Magnetically lock the iron oxide particles and aspirate
the unbound solution.
[0070] 10. Dispense 60 .mu.L of neutralization buffer (460 mM
Bicine) into the tube and mix the sample 15 times.
[0071] 11. Magnetically lock the iron oxide particles and aspirate
the unbound solution.
[0072] 12. The eluted samples are ready for SDA assay (50 .mu.L of
sample per assay). TABLE-US-00001 Sample Plasma Plasma Plasma
Plasma Assay Assay buffer buffer Target HIV HIV HIV HIV RNA RNA
particles particles particles particles transcripts transcripts
(copies/rxn) 200 200 200 200 50 0 Treatment ProK ProK KOH/Triton
KOH/Triton NA NA Temperature 70.degree. C. 70.degree. C. 70.degree.
C. RT NA NA Binding Acid Glycine.HCl H.sub.3PO.sub.4
H.sub.3PO.sub.4 H.sub.3PO.sub.4 Pos. Ctl. Neg. Ctl. 16288 15082
21231 25877 54900 31 15172 36351 22749 33803 34578 29 14140 31430
21044 33007 47591 0 18146 35206 24992 33360 60299 10 18466 38333
37972 32719 62607 27 7656 38215 35586 37108 61437 26 19799 34641
33518 31997 49383 30 8220 33189 27612 36132 60305 29 Average 14736
32806 28088 33000 53888 23 SD 4282 7051 6308 3148 9008 11 CV % 29
21 22 10 17 47
[0073] The results demonstrate that RNA can be extracted from HIV
particles in plasma treated using an alkaline agent and a detergent
according to the present invention. The extracted RNA can be used
in nucleic acid amplification assays such as SDA. The combination
of the chemical treatment of plasma and use of phosphoric acid as a
binding acid had equivalent or better results than use of the
enzyme digestion method.
[0074] The method of the invention is advantageous in that it does
not rely on the use of enzymes. It is therefore less expensive and
would generally be expected to be a more robust process. It also
has the added advantage of being effective at room temperature and
not requiring extended periods of time for incubation. The process
would also be expected to be applicable to DNA and RNA extraction
from a number of biological samples.
[0075] Note that this experiment utilized diluted plasma (62.5%).
Attempts to utilize 100% plasma treated using the protease method
resulted in sample coagulation during enzyme treatment, thereby
rendering nucleic acid extraction extremely difficult and
inefficient. However, use of the chemical "no protease" method of
the invention improves sample solubility throughout the nucleic
acid extraction process, thereby allowing extraction from a greater
percentage of sample and, hence, greater sensitivity of
detection.
[0076] As discussed herein, the volume of the sample can be varied.
For example, the sample can be diluted with buffers such as 30 mM
potassium phosphate before or after treatment. Incubation time and
temperature can also be varied. The concentration and type of
alkaline agent and detergent can be varied. The protocol can be
used with manual or automated nucleic acid extraction methods. The
type and concentration of acid can be varied. The extracted nucleic
acids can be used for a variety of down stream applications.
[0077] While the invention has been described with some
specificity, modifications apparent to those with ordinary skill in
the art may be made without departing from the scope of the
invention. Various features of the invention are set forth in the
following claims.
* * * * *